1. Field
This disclosure relates to measuring and testing, and more particularly to testing of solder balls and similar structures, such as found in a ball grid array.
2. Background
Because ball grid arrays (BGAs) have a wide application in electronic packaging, the packaging strength of BGAs to the attachment substrate is crucial for industry. Industry uses a test procedure called a “single ball shear test”, which provides a simple and efficient technique for evaluating the quality of solder balls. Experimental observations from low shear rate tests of solder joints are not accurate predictors of failure behaviour at high strain rates. That is because low shear rate tests of solder joints cannot accurately predict the mode of deformation and failure behavior at high strain rates. Due to strain rate effect, brittle failures often take place when the solder joints are subjected to dynamic loadings, and such brittle failures may not be seen under low strain rate shear tests.
Thus, it is desired to develop an improved test procedure capable of evaluating the impact strength characterization of component parts. One such example is a procedure for evaluating the impact strength characterization of solder joints. Such impact strength characterization becomes critical during package design and manufacturing for high reliability. This is particularly true for lead-free solder, for example, lead-free solder used in handheld devices.
Conventional techniques of testing solder balls use a linear accelerating system to shear the solder ball at different speeds. FIGS. 1A and 1B are schematic diagrams showing the movement of a tester tip against a solder ball. As FIGS. 1A and 1B depict, the tip moves in the linear direction from a significant distance. At an expected speed, the tip will shear the solder ball, resulting in the removal of the solder ball (FIG. 1B). FIG. 2 is a graph showing measured load vs. displacement. During this impact situation, the force versus displacement curve will be recorded, resulting in a graph as shown in FIG. 2. The load may be measured at the tip's holder or at the clamp for the substrate to which the solder ball is attached. From the curve depicted in FIG. 2, the resistance of shearing the solder ball can be observed.